Evaluation of diagnostic tests for hypocalcemia in critically ill newborns

Objective. To determine sensitivity (Sn), specificity (Sp), positive and ne gative predictive values (PPV, NPV) of total and calculated calcium and of QTc and QoTc intervals for the diagnosis of hypocalcemia in critically ill newborns. Setting. A neonatal intensive care unit. Methods. We included all newborn less than 28 days of age; we excluded those with calcium treatment , hypomagnesemia or congenital heart disease. Serum levels of total calcium , albumin and ionic calcium were measured as well as the QTc and QoTc inter vals. Values for Sn, Sp, PPV and NPV were calculated acoording to cutoff po ints of the literature and with those of our receptor operating curves (ROC ). Ionic calcium was considered the gold standard (hypocalcemia < 1.10 mmol /L). Results. We included 53 newborns; 21/53 (40%) had hypocalcemia. Clinic al features were similar among patients with or without hypocalcemia. For t otal calcium the Sn was 47%; Sp = 87%; PPV = 71% and NPV = 72%. For calcula ted calcium there values were: 55, 75, 57 and 73; for QoTc: 47, 81, 61 and 70%; and for QTc: 19, 87, 50 and 62% respectively. With the ROC values the Sn for total calcium and QTc was improved. Conclusions. Among critical ill newborns, total and calculated calcium were better in identifying patients with hypocalcemia whereas QTc and QoTc were better in those without hypocal cemia.